This invention relates to an exhaust system for an engine in which system a plurality of exhaust pipes are connected to a combined portion and a common exhaust pipe is connected to a downstream end of the combined portion.
There has been generally known an exhaust system in which a plurality of exhaust pipes are connected to a combined portion and a common exhaust pipe is connected to a downstream end of the combined portion. This system is found in a V-shaped engine or the like. For example, the system disclosed in Japanese Unexamined Utility Model Publication No. 3-32117 is constructed as follows. An exhaust manifold is mounted on an outer side wall of each bank of a V-shaped engine longitudinally mounted so that an engine output shaft extends in a lengthwise direction of an automotive vehicle. An exhaust pipe is connected to each exhaust manifold. These exhaust pipes are bent from opposite sides of a transmission housing toward the center with respect to a widthwise direction of the transmission housing at the back side of the engine. These exhaust pipes are connected to a combined portion behind the transmission housing and a common exhaust pipe is connected to a downstream end of the combined portion.
In the system disclosed in the above publication, the vibrations from the engine, the transmission, and the like are transmitted to the exhaust pipes and the common exhaust pipe, with the result that an exhaust pipe assembly including the exhaust pipes and common exhaust pipe vibrates. The vibrations generated in this manner, especially three-dimensional vibrations, are likely to exert a large force on the exhaust pipe assembly and a portion supporting this assembly.
More specifically, the exhaust pipe assembly is supported on the transmission housing normally at an intermediate portion of the common exhaust pipe. Since the exhaust pipes are both bent three-dimensionally and connected to the combined portion, the engine vibration is transmitted to the exhaust pipes. Further, the vibration generated due to the power plant bending is transmitted to the common exhaust pipe through the supporting portion thereof fixed to the transmission housing. These vibrations act each other vertically and laterally, thereby causing the exhaust pipe assembly to generate a complicated three-dimensional vibration. Due to this vibration as well as a torsion, a large stress acts on the exhaust pipe assembly and the supporting portion of the transmission housing where the common exhaust pipe is supported. This is an unfavorable factor in improving the durability of the exhaust pipe assembly and the supporting portion.